The present invention relates to a method and apparatus for cutting a rare earth alloy. More particularly, the present invention relates to a method and apparatus for cutting a rare earth alloy with a wire having super abrasive grains such as diamond grains stuck thereon.
Conventionally, a technique of cutting an ingot of silicon with a wire saw to slice the ingot into a large number of wafers has been developed. Japanese Laid-Open Publication No. 6-8234, for example, discloses this technique. In accordance with this technique, a large number of wafers, each having a constant thickness, can be simultaneously sliced from an ingot by cutting the ingot with a multi-wire running while supplying some slurry containing abrasive grains thereto.
On the other hand, in accordance with a known technique, an ingot of a rare earth alloy is sliced using a rotating slicing blade, for example. However, such a technique using a slicing blade requires an undesirably large cutting margin, because the cutting edge of a slicing blade is thicker than that of a wire. Therefore, such a technique fails to contribute to efficient use of valuable resources.
A rare earth alloy is suitable for use as a magnet material, for instance. A magnet has found a wide variety of applications and is now broadly used for various types of electronic appliances. Under the circumstances such as these, it is highly desirable to cut down on the manufacturing cost per rare earth magnet. And the cost would be considerably reduced if a great number of wafers could be produced simultaneously from an ingot of a rare earth alloy such that a cutting margin can be reduced by the use of a wire saw and that each wafer has a constant thickness.
However, no one has ever reported on successfully cutting a rare earth alloy in accordance with a practical wire-saw technique. The present inventors experimentally cut an ingot of a rare earth alloy with a wire saw of free abrasive grain type. As a result, we found that since a slurry-circulating pipe was clogged up in a very short amount of time with fine powder and grinding debris (i.e., swarf or sludge) involved with wire sawing, no slurry could be supplied to the wire after that, and the wire eventually snapped. If the slurry was entirely replaced every several hours in order to avoid this problem, wire sawing had to be suspended for a while every time the slurry was replaced. Thus, such machining is not suitable for mass production and it is virtually impossible to put such machining into practice. We also observed that since the sludge was easily deposited in a cut groove, the cutting resistance noticeably increased and the wire was even more likely to snap as a result. Furthermore, the cutting accuracy was found considerably deteriorated because various unwanted operating failures frequently happened during the cutting process. For example, the wire often disengaged from rollers, around which the wire was wound, because the sludge was also likely to be deposited on the grooves of the rollers. None of these problems has ever been observed during cutting an ingot of silicon or glass in accordance with a conventional wire saw technique.
The wire saw of free abrasive grain type where abrasive grains float in slurry has a problem of its own as follows. Free abrasive grains tend to roll on the cutting area during the cutting process. It is therefore difficult to increase the amount of cutting per unit time (cutting speed). In particular, when a rare earth alloy is cut with the wire saw of free abrasive grain type, the cutting speed greatly decreases, because a rare earth alloy is a rigid, tenacious material less easy to be cut, compared with silicon and glass.
Japanese Laid-Open Publication No. 8-126953 discloses a technique where an ingot of silicon is cut with a wire of fixed abrasive grain type using water as a coolant. When this technique is applied to cutting of a rare earth alloy, however, the same problems as those described above in relation with the free abrasive grain type occur, because sludge of a rare earth alloy is difficult to be carried out from the cutting grooves.
A prime object of the present invention is providing a method and apparatus for cutting a rare earth alloy to ensure a long-time continuous operation by preventing wire snapping and improve the cutting speed.
Another object of the present invention is providing a method for manufacturing rare earth magnets using the method for cutting a rare earth alloy.
Still another object of the present invention is providing a voice coil motor including a rare earth magnet manufactured by the method of the present invention.
The method for cutting a rare earth alloy of the present invention uses a wire having abrasive grains stuck thereon. The method includes the step of cutting the rare earth alloy while supplying a cutting fluid having a predetermined kinematic viscosity between the wire and the rare earth alloy.
Preferably, the kinematic viscosity of the cutting fluid supplied between the wire and the rare earth alloy is in a range of 6.0 mm2/s to 100.0 mm2/s.
In a preferred embodiment, the cutting fluid is a cutting oil, and the cutting oil preferably has a viscosity at 40xc2x0 C. in a range of 4.0 to 40.0 mPaxc2x7sec.
In another preferred embodiment, the cutting fluid is a glycolic water-soluble cutting fluid, and the glycolic water-soluble cutting fluid preferably has a kinematic viscosity at 25xc2x0 C. in a range of 10.0 mm2/s to 67.0 mm2/s.
Preferably, the kinematic viscosity of the cutting fluid is controlled by control of the temperature of the cutting fluid.
Preferably, the method further includes the steps of: recovering or collecting the cutting fluid containing sludge of the rare earth alloy generated during the cutting of the rare earth alloy; and removing the sludge from the recovered or collected cutting fluid before the control of the temperature of the cutting fluid.
The control of the temperature of the cutting fluid preferably includes the steps of: thermoregulating part of the cutting fluid from which the sludge has been removed; and mixing the thermoregulated part of the cutting fluid and the remaining cutting fluid that has not been thermoregulated, the mixed cutting fluid being supplied between the wire and the rare earth alloy.
Preferably, the sludge of the rare earth alloy generated during the cutting of the rare earth alloy is separated from the cutting fluid with a magnetic force.
Preferably, a magnetic separator capable of generating a magnetic force of 0.27 tesla or more is disposed in a region for collecting the sludge from the cutting fluid.
In a preferred embodiment, the cutting is performed using a wire saw machine comprising: a plurality of rollers supported rotatably, each of the rollers having a plurality of ring-shaped grooves formed on an outer circumference of the roller at a predetermined pitch; and driving means for rotating the rollers for allowing the wire wound along the grooves of the rollers to run.
Preferably, the rare earth alloy is cut with the wire while the rare earth alloy is moved from a position above the wire toward a position below the wire.
Preferably, the rare earth alloy is divided into a plurality of blocks and secured together, and at least part of the supply of the cutting fluid is performed through gaps between the plurality of blocks.
The method for manufacturing rare earth alloy plates of the present invention includes the steps of: producing an ingot of a rare earth alloy; and separating a plurality of rare earth alloy plates from the ingot by any of the method for cutting a rare earth alloy described above.
The method for manufacturing rare earth magnets of the present invention includes the steps of: producing a sintered body from rare earth magnetic alloy powder; and separating a plurality of rare earth magnets from the sintered body by any of the method for cutting a rare earth alloy described above.
The voice coil motor of the present invention includes the rare earth magnet manufactured by the method for manufacturing rare earth magnets described above.
In a preferred embodiment, the thickness of the rare earth magnet is in a range of 0.5 to 3.0 mm.
The apparatus for cutting a rare earth alloy of the present invention cuts a rare earth alloy with a wire. The apparatus includes: a wire having abrasive grains stuck thereon; and means for supplying a cutting fluid having a predetermined kinematic viscosity between the wire and the rare earth alloy.
Preferably, the kinematic viscosity of the cutting fluid supplied between the wire and the rare earth alloy is in a range of 6.0 mm2/s to 100.0 mm2/s.
Preferably, the apparatus further includes viscosity control means for controlling the kinematic viscosity of the cutting fluid supplied between the wire and the rare earth alloy.
The viscosity control means preferably controls the kinematic viscosity of the cutting fluid by control of the temperature of the cutting fluid.
The viscosity control means preferably includes: a vessel for storing the cutting fluid; a thermoregulator for controlling the temperature of at least part of the cutting fluid stored in the vessel; and a stirrer for stirring the cutting fluid stored in the vessel.
Preferably, the apparatus further includes a magnetic separator for separating sludge of the rare earth alloy generated during the cutting of the rare earth alloy from the cutting fluid with a magnetic force.
In a preferred embodiment, the magnetic separator generates a magnetic force of 0.27 tesla or more in a region for collecting the sludge from the cutting fluid.
As used herein, the term xe2x80x9ccutting fluidxe2x80x9d is defined as including a water-insoluble cutting fluid (also called xe2x80x9ccutting oilxe2x80x9d) and a water-soluble cutting fluid, excluding cutting water that contains water as a main component and has a kinematic viscosity of about 1 mm2/s.